A general method of producing nylon by using diamine is a chemical process of using 1,4-diaminobutane and hexamethylenediamine as raw materials. These raw materials are produced from petroleum-based organic compounds. Therefore, as environmental regulations are strengthened, market demand for alternative materials produced through bio-based routes is growing.
Meanwhile, cadaverine is a diamine organic compound composed of 5 carbons which has a molecular formula of NH2(CH2)5NH2, and it may be a raw material for nylon 5,6. If bio-based preparation of cadaverine is possible, it is expected that a variety of nylons can be produced while satisfying the market demand for bio-based materials.
Regarding bio-based production of cadaverine, studies on bioconversion of lysine were widely known before the 1940's (Gale E. F., Epps H. M. 1944. Studies on bacterial amino-acid decarboxylases. Biochem J. 38, 232-242). In a key stage of the bioconversion, lysine decarboxylase is an enzyme that produces cadaverine from lysine (FIG. 1). Activity of lysine decarboxylase in many different microorganisms has been reported, and lysine decarboxylase, of which specific activity (mmol/min/mg) is known, is derived from four kinds of microorganisms (Escherichia coli, Bacterium cadaveris, Glycine max, and Selenomonas ruminantium). Of them, lysine decarboxylase derived from Escherichia coli is evaluated as the lysine decarboxylase having the highest activity, and the enzyme used in practical production is also limited to CadA which is derived from Escherichia coli (Japanese Patent No. 2005-147171, European Patent No. 2004-010711, and Japanese Patent No. 2002-257374). However, production of cadaverine by reacting lysine with lysine decarboxylase generates carbon dioxide by decarboxylation of lysine, and produces a divalent cation, cadaverine from a monovalent cation, lysine thereby increasing pH during the reaction. Thus, when the enzymatic reaction of lysine decarboxylase occurs, pH is changed, which generates a problem of efficiency reduction. Further, the enzyme may be denatured by an acid produced in a reaction solution, or a base, thereby losing its activity.
Accordingly, the present inventors discovered a novel lysine decarboxylase having stability against high temperature and pH, and found that the lysine decarboxylase may be expressed in a microorganism belonging to Escherichia sp., thereby completing the present invention.